# ---
# title: 1370. Increasing Decreasing String
# id: problem1370
# author: Tian Jun
# date: 2020-10-31
# difficulty: Easy
# categories: String, Sort
# link: <https://leetcode.com/problems/increasing-decreasing-string/description/>
# hidden: true
# ---
# 
# Given a string `s`. You should re-order the string using the following
# algorithm:
# 
#   1. Pick the **smallest** character from `s` and **append** it to the result.
#   2. Pick the **smallest** character from `s` which is greater than the last appended character to the result and **append** it.
#   3. Repeat step 2 until you cannot pick more characters.
#   4. Pick the **largest**  character from `s` and **append** it to the result.
#   5. Pick the **largest**  character from `s` which is smaller than the last appended character to the result and **append** it.
#   6. Repeat step 5 until you cannot pick more characters.
#   7. Repeat the steps from 1 to 6 until you pick all characters from `s`.
# 
# In each step, If the smallest or the largest character appears more than once
# you can choose any occurrence and append it to the result.
# 
# Return _the result string_ after sorting `s` with this algorithm.
# 
# 
# 
# **Example 1:**
# 
#     
#     
#     Input: s = "aaaabbbbcccc"
#     Output: "abccbaabccba"
#     Explanation: After steps 1, 2 and 3 of the first iteration, result = "abc"
#     After steps 4, 5 and 6 of the first iteration, result = "abccba"
#     First iteration is done. Now s = "aabbcc" and we go back to step 1
#     After steps 1, 2 and 3 of the second iteration, result = "abccbaabc"
#     After steps 4, 5 and 6 of the second iteration, result = "abccbaabccba"
#     
# 
# **Example 2:**
# 
#     
#     
#     Input: s = "rat"
#     Output: "art"
#     Explanation: The word "rat" becomes "art" after re-ordering it with the mentioned algorithm.
#     
# 
# **Example 3:**
# 
#     
#     
#     Input: s = "leetcode"
#     Output: "cdelotee"
#     
# 
# **Example 4:**
# 
#     
#     
#     Input: s = "ggggggg"
#     Output: "ggggggg"
#     
# 
# **Example 5:**
# 
#     
#     
#     Input: s = "spo"
#     Output: "ops"
#     
# 
# 
# 
# **Constraints:**
# 
#   * `1 <= s.length <= 500`
#   * `s` contains only lower-case English letters.
# 
# 
## @lc code=start
using LeetCode

## add your code here:
## @lc code=end
